Coiled tubing is used in maintenance tasks on completed oil and gas wells and drilling of new wells. Operations with coiled tubing (“CT”) involving upstream oil and gas recovery requires the capability to make butt or girth joints in the tubing for a variety of reasons. In particular, for offshore applications, the limitations on crane hoisting load capacities necessitates the assembly of two or more spools of coiled tubing once they have been delivered on deck.
There are two basic means to effect a girth joint connection. One way is by welding and the other involves the use of a spoolable mechanical connection. This may include the need for advanced machine welding processes, namely orbital tungsten inert gas (“TIG”), for onshore welded connections. These exhibit a low cycle fatigue (“LCF”) life that is in the range of 50% to 60% of non-welded tubing. This magnitude of fatigue performance is twice the minimum value of what is generally accepted for welded connections made by the manual TIG process, which is 25% for manual TIG.
TIG welding requires skilled labor and great care in edge preparation. It is also susceptible to welding flaws if the shielding gas became deflected from a crosswind. For offshore applications where storms are frequent, an enclosed habitat would be required. In general, the logistics of performing orbital TIG offshore is significantly more complex.
The coiled tubing industry has developed many different and successful mechanical methods for joining coiled tubing to fittings and attachments. Among these are the familiar roll-on and dimple connectors that have been in service for many years. However, the development of a mechanical connector that can be plastically spooled repetitively on and off a working reel, has not met with similar success. The number of plastic bending cycles without failure of these mechanical connections was insufficient from both a practical, economic and safety point of view. This means that their LCF life was less than the 25% of tubing life achievable on average for manual TIG girth welds.
Therefore, a need exists for a connector that has elastic and plastic bending response that is optimized. Moreover, these connectors need an increased LCF life, better axial loading, and better corrosion resistance compared to that of the coiled tubing material and connectors of the prior art.